Commonly assigned, copending U.S. patent application Ser. No. (TUC9-2000-0024-US1) is incorporated for its showing of a distributed control system for an automated data storage library.
This invention relates to automated data storage libraries, and, more particularly, to the queuing of received work requests for a library.
The typical automated data storage library comprises an accessor having a gripper for accessing data storage media, and which is moved in the X direction and in the Y direction for accessing the data storage media and moving the media between storage shelves and data storage drives.
Also typically, the host system, such as a host server, communicates with a central controller for the library, either directly or through one or more data storage drives, providing commands to access particular data storage media and move the media between the storage shelves and the data storage drives, as well as I/O shelves and pass thru slots. The commands may be logical commands identifying the media and/or logical or physical locations for accessing the media. The central controller includes a processor for receiving the commands and establishing a work queue for the library. As the work queue is processed, the processor converts the commands to physical movements of the accessor, and transmits signals for operating servo motors.
It is desirable to allow for expansion in the library to include additional storage shelves and data storage drives and a second accessor. As an example, an IBM 3494 automated data storage library is scaleable up to 2 end frames, each with an accessor, and 14 extension frames of storage shelves between the end frames. Typically, both accessors travel on similar paths alongside the storage shelves and the data storage drives. Hence, to avoid interference, the central processor designates one accessor as active and the other as inactive, and operates only the active accessor. Thus, the inactive accessor serves as a backup in case the active accessor fails or is taken out of service. Alternatively, the central processor breaks the library into zones of storage shelves and data storage drives and separately operates the accessors to access data storage media in the respective zones.
The central processor and its communication line to the accessor, however, each comprises a single point of failure, failure of which would make the library unavailable for use.
Disclosed are a work queuing system and method for an automated data storage library which increases the availability of the library without requiring changes to existing host software. The library has a plurality of storage shelves for storing data storage media, at least one data storage drive, and at least one accessor for accessing and delivering data storage media among the storage shelves and the data storage drives in response to work requests. The work queuing system comprises a communication processor node for receiving the work requests and for broadcasting the work requests, e.g., over a common bus network, to a plurality of work processor nodes coupled to the communication processor node and coupled to each other. Each work processor node responds to the broadcast work requests, establishing a work queue of jobs. At least one of the work processor nodes selects ones of the jobs in the work queue for the accessor(s). The work processor node directs an accessor to conduct a selected job, and the work processor node broadcasts information regarding the selected job to other of the work processor nodes, such as completion of the job, so that the work queues may be maintained in synchronism.
To maintain the work queues in synchronism, each of the other work processor nodes additionally, upon receiving the broadcast job information, removes the selected job from its work queue.
For a fuller understanding of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.